Ditto with B.O.B on your tiling, jawesome

Dont even think of changing the contrast of that background! it has a godly awesome arcade platformer feel to it that is worth it's bits in gold :p
I think however low the contrast is (and I think it's fine) the platforms are flat and obvious enough that realistically nobody playing it could feel confused. I'd hate to change the mockup, but if I absolutely had to I'd just light up the foreground platforms, there's just something soooo beautiful about those uncontrasted shadows
However, you MUST do the kind of upped contrast Ptoing suggested for the background on the characters instead. They just blend in way badly.
Animationwise, they all look quite evidently boxed in, the vulture most of all. it seems as if they KNOW they're inside a ## by ## field and wont move too much so as to not exceed that limit. I think you went overboard with taking advantage of all your space and didnt leave room for your actions...hope you learnt your lesson you little punk, you

Dude, I like the feel of the background so much...but I cant place what it reminds me of. Did you think of any specific game as you drew it?